Check frequency
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From: John Fields on 20 Dec 2009 09:38 On Sun, 20 Dec 2009 11:49:34 +1100, "Phil Allison" <phil_a(a)tpg.com.au> wrote: > >"John Fields, Autistic " > >>>> With the crystal running at about 32768 Hz, how do you propose to make >>>> one cycle last for 100 seconds? >>> >>>Look up 'Lissajous'. >> >> --- >> Why would you snip, from my post,: >> >> "Furthermore, Lissajous figures are generated by signals applied to the >> X and Y axes of the scope, so how do you propose to see anything >> meaningful with, say, Y running at 32768 Hz and X running at 100 >> seconds?" >> >> and then insert that: "Look up 'Lissajous'" crack? >> --- > >** Errr - because you repeatedly failed to comprehend how Lissajous >patterns are commonly used to compare two frequencies ?? --- Don't be absurd. What I question is the use of Lissajous figures in order to determine frequencies accurately to within a few ppm more economically than by using a frequency counter. This isn't the 1920's any more, you know. --- > Is the great JF completely ignorant of a such a simple technique. --- Hardly; I probably learned about it while you were still floating around in your mother's alimentary tract. --- > Must be so - everything he says screams it. --- There are none so deaf as those that will not hear. --- >> Indeed, but looking over your post again, you mentioned nothing about >> the accuracy of the reference, but instead stated that a 100 second >> measurement window accurate to 0.1 Hz would yield 0.001 Hz accuracy, >> which is clearly not true. > >Here is the idea: > >" If you have a suitable reference frequency source, you can watch the >pretty Lissajous figure on an X/Y oscilloscope (no dual channel, no >counter) and if it goes through a cycle in 100 seconds, with 0.1 second >stopwatch accuracy, you've just made a frequency measurement with >0.001 Hz accuracy. For your 32 kHz crystal, that's a second per year >kind of accuracy. > >A frequency counter is a convenient and quick solution, but >it is NOT required nor is it superior in accuracy. " > > >** Fraid it is all true..... > >The demented JF has forgotten how to think analogue. > >Cos he has forgotten how to think at all. --- Ho-hum... JF
From: John Fields on 20 Dec 2009 12:06 On 20 Dec 2009 08:25:52 GMT, Jasen Betts <jasen(a)xnet.co.nz> wrote: >On 2009-12-19, John Fields <jfields(a)austininstruments.com> wrote: > >> I would, but I'm fresh out of watch crystals. >> >> Anyway, just for grins I put together a 30 turn probe and held it close >> to a 10k resistor with a 32768Hz TTL square wave going through it. >> >> I could see the signal, just barely, against fluorescent background >> noise, but the counter liked the noise better. > >use a tuned probe. 32768Hz crystals work good for probes. --- So does an electret mic. :-) JF
From: whit3rd on 20 Dec 2009 17:42 On Dec 19, 4:13 pm, John Fields <jfie...(a)austininstruments.com> wrote: > ... looking over your post again, you mentioned nothing about > the accuracy of the reference, but instead stated that a 100 second > measurement window accurate to 0.1 Hz would yield 0.001 Hz accuracy, > which is clearly not true. What I wrote, was that one could watch a Lissajous pattern evolve and time it with a stopwatch with 0.1 second accuracy. A stable pattern indicates exact small-integer-ratio frequency matching, and an evolving pattern indicates a deviation from the match. So, for someone working with a trimmer, you get immediate visual feedback when looking at a Lissajous display, and the trim is quickly done. If there's a drift, as I described, you can use simple easily available tools (a stopwatch) to achieve quite remarkable precision. That '.001 Hz' was not a joke, nor an error. As to the accuracy of the 'reference', it was my thought that a crystal out of the box would have 5 figure accuracy, maybe 6, and that trimming it would require a reference with much more than that (8 figures being a good high target). My frequency counters aren't that good, and the required gate times aren't friendly to tweaking-as-you-watch even if they were. I believe tuning-fork watch crystals are trimmed at the factory with laser ablation of the metal (mass) on the tines, and, with the recommended oscillator circuitry, should do well without any adjustment. Aging and temperature drifts which aren't trimmable are likely to be significant.
From: Phil Allison on 20 Dec 2009 17:50 "John Fields, Autistic LIAR " >>> With the crystal running at about 32768 Hz, how do you propose to make >>> one cycle last for 100 seconds? >> >>Look up 'Lissajous'. > > --- > Why would you snip, from my post,: > > "Furthermore, Lissajous figures are generated by signals applied to the > X and Y axes of the scope, so how do you propose to see anything > meaningful with, say, Y running at 32768 Hz and X running at 100 > seconds?" > > and then insert that: "Look up 'Lissajous'" crack? > --- ** Errr - because you repeatedly failed to comprehend how Lissajous patterns are commonly used to compare two frequencies ?? The great JF is completely ignorant of a such a simple technique. > Indeed, but looking over your post again, you mentioned nothing about > the accuracy of the reference, but instead stated that a 100 second > measurement window accurate to 0.1 Hz would yield 0.001 Hz accuracy, > which is clearly not true. Here is the idea: " If you have a suitable reference frequency source, you can watch the pretty Lissajous figure on an X/Y oscilloscope (no dual channel, no counter) and if it goes through a cycle in 100 seconds, with 0.1 second stopwatch accuracy, you've just made a frequency measurement with 0.001 Hz accuracy. For your 32 kHz crystal, that's a second per year kind of accuracy. A frequency counter is a convenient and quick solution, but it is NOT required nor is it superior in accuracy. " ** Fraid it is all true..... The demented JF has forgotten how to think analogue. Cos JF has autistic dementia and cannot think at all. ..... Phil
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